Control apparatus



Dec. 21, 1954 A. E. BAAK CONTROL APPARATUS Original Filed Oct. 24. 19463 Sheets-Sheet 1 Dec. 21, 3954 A. E. BAAK 23,913

CONTROL APPARATUS Drizinal Filed Oct, 24. 1946 3 Sheets-Sheet 5,

g Gttomg u Re. 23,913 Reissued. Dec. 21, 1954 CONTROL APPARATUS AlbertE. Baak, Pacific Palisades, Calif., assignor to Minneapolis-HoneywellRegulator Company, Minneapolis, Minn., a corporation of DelawareOriginal No. 2,585,295, dated February 12, 1952, Serial No. 705,261,October 24, 1946. Application for reissue December 1, 1952, Serial No.323,527

18 Claims. (Ci. 981.5)

Bt'ifiififl' enclosed in heavy brackets appears in the original patentbut forms no part of this reissue specification; matter printed initalics indicates the additions made by reissue.

The present invention is directed to improved control apparatus for thepressurizing of aircraft cabins.

Assuming an adequate supply of air for an aircraft cabin, the pressurewithin the cabin can be controlled by regulating the outflow of the air.The pressure to be maintained will depend upon the adjustments of thesystem, the characteristics of the aircraft, the altitude to be attainedby the airplane, the elevation of the landing field to be used, andother such factors. In addition, the rate of change of pressure must bekept within the desired limits, as sudden changes in pressure from anycause cannot be permitted.

In view of the many requirements of a successful system, is it aprincipal object of this invention to provide improved cabin pressurecontrol apparatus for aircraft.

It is an object to provide improved cabin pressure control apparatusoperable to maintain any desired pressure in excess of atmosphericpressure, within a predetermined limiting differential.

His :1 further object to provide cabin pressure control apparatus ofsuch nature that increases in pressure differential are at a controlledrate regardless of the variations in altitude of the aircraft.

It is an additional object to provide automatic cabin pressure controlapparatus that can be manually actuated if desired.

7 It is an object to provide control apparatus which may be eitherautomatic in operation or manually actuated and which will indicate theposition of the controlled device under either sort of operation.

It is a further object to provide control apparatus including means forshifting the control point of said apparatus to an adjusted value at atimed rate and which also includes means for indicating the controlpoint at any particular instant.

It is an additional object to provide control apparatus including acontrol point index for continuously indicating the actual control pointand means for actuating the said index when the controlling device iseither manually or automatically operated.

It is also an object to provide control apparatus for a pressurizedaircraft cabin which includes a control point adjusting means whichkeeps step with the pressure in the aircraft cabin when the airplanedescends below the altitude setting of the cabin so that a subsequentincrease in altitude of the aircraft will result in the pressure of thecabin resuming its controlled value at a controlled rate.

'It is a similar object to provide control apparatus for a pressurizedaircraft cabin which includes a control point adjusting means and indexwhich keeps step with the actual pressure in the cabin when the aircraftis operated in an unsupercharged condition.

It is a further object to provide cabin pressure control apparatus soarranged that it cannot be shifted from a pressurized condition to anonpressurized condition, or the reverse, unless the outflow valve iswide-open so that there can be no sudden pressure changes.

It is an object to provide cabin pressure control ap paratus which isinherently safe and dependable.

' It is a further object to provide control apparatus wherein thecontrol can be shifted from automatic to manual and back to automaticwithout pressure changes iii) due to the said shifting, and whereinpressure changes due to the operation of the automatic control will beat a timed rate.

It is also an object to provide control means for the pressure controlapparatus, pressure seals, and the like, of an aircraft wherein it isimpossible to actuate this apparatus in a manner to suddenly decompressthe said cabin.

It is a further object to provide pressure control apparatus for anaircraft wherein signal means are provided for showing power failure,low pressure, an open valve, and the use of the manual override control.

These and other objects will become apparent upon a study of thefollowing specification and drawings wherein:

Figure l is a schematic showing of the present control equipment appliedto a pressurized aircraft cabin;

Figure 2 is an elevation view of the control point selector and index ofthe control panel, with parts broken away to better show theconstruction;

Figure 3 is a sectional end view of the aforementioned control pointselector;

Figure 4 is a sectional elevation of the motorized valve used forcontrolling outflow;

Figure 5 is a sectional end view of the manual override mechanism foroperating the aforementioned valve and for indicating the position ofthe valve; and

Figure 6 is a schematic wiring diagram of the present control apparatus.

Referring to Figure l, pressurized aircraft cabin 10 is schematicallyshown in its relation with compressors 11, ram air inlets 12, supplyduct means generally designated 13, recirculating duct means 14, outflowvalve means 15, and other control apparatus to be specificallyenumerated. The intake portions of compressors 11, and ram air inlets 12are preferably located in a frontal portion of the airplane, such asalong the leading edges 16 of the aircraft wings. The dischargefromcompressors 11 may be dumped through exit means 17 or may besupplied through duct means 13 to the cabin, as shown. Adjustable dampermeans 18 controlled by reversible motor means 19 determine whether theair will be dumped or directed through conduit means 13 to the cabin.Ram air entering through inlets 12 may be directed through ducts 20 toduct means 13 or through ducts 21 which supply cooling air to heatexchangers 22. The flow of air through ducts 20 is either permitted orprevented by pressure seal damper means 23 controlled by reversiblemotor means 24. The flow of air through ducts 21 is controlled by dampermeans'249 but they form no part of this invention and will not befurther described.

The air supplied cabin 10 is diverted directly to the said cabin throughduct means 13 when diverting damper means 25 is in the position shownbut may be directed through a branch duct 26 past circulating fan 27when damper means 25 is adjusted to its opposite position. Damper means25 is operated by reversible motor means 28. Recirculating duct means14, as its name implies, receives air from the cabin 1t) and delivers itinto duct 26 where flow is induced by circulating fan means 27. Undersome conditions, recirculation may be prevented by damper 29 and thereturn air may be dumped to the outside atmosphere through ventilationoutlet 30 controlled by damper means 31. Damper means 29 and 31 areoperated by reversible motor means 32 and 33, respectively. Motor means19, 24, 28, 32 and 33 are substantially alike and comprise conventionalcapacitor type reversible control motors operating through suitable geartrains and including suitable internal limit switches. These motors areenergized by the volt 400 cycle current supply of the airplane, theenergization of these motors being controlled in a manner to bedescribed. As will be made clear in the succeeding description, damper31 is closed when the cabin is pressurized, as are pressure seals 23,hence the only controlled outflow for the air introduced to the cabinmust be through valve means 15. Therefore, the means controlling valve15 controls the pressure in the aircraft cabin.

The control equipment for outflow valve 15 includes a differentialpressure controller 41, an absolute pressure controller 42, a maincontrol panel 43, a main switching means, a manual override device 45,an amplifier 46, anda-junction box47. This-apparatus isshownschematically connected, with the main switching means 44 alsobeing shown in its schematicrelation with theaforementionedtcontrolimotors. whilelthegpresent control compon n'tsaresshownwschematically located :in rthe cabin of the craft, this is nota necessary arrangement, but :rather is merely-1a convenient one.aCertainxof fthe components, suel tas the lamplifier, junction box, andother such means my be lQGfltfidtll'l HOTlgPl'QSSUfiZCdPOI'llOnS of the:aircraft, fs irei- Diiferential pressure controller 41, as shown inFigure 6,-eomprises a- =be1lows :51 having :itsoutside exposed to thepressureof-=the:aifr withinihe cabin and the inside offtlic fiamecnnectetl" by-tuhe means 52 to the outside atmosphere. -Bellows.SLI-isconnectedby iink 53 to a pivoted switch;means.54,tsaidswitchmeans fiihaving a blade .5 -\coacting -with--1contact.56 ortcontact 57.-'A sec ondblade 58 carried by switch means 54 coacts withcontact 59.suitabletension=spring=60 biases blade 54 to theright in suchamannerthat-blade 55 is in engagement with .conrac't 56 at Etllldifferential pressures below 4.6 pounds-persquare inch;-b]adc.55 engagescontact 57 at a differential pressure .of' 4i7 pounds'per square inch,and blade :58.engages .contact 59,-at-diiferential pressures at or inexcess of 4.8 pounds per square inch, these values beingillustrativetonly.

Absolute pressure responsive 'device 42 in Figure 6, comprisesancvacuatedbellows 62 having anv'internal expansible spring, lriot,shown. .Bellows '62 is connected through 'link'63 toi'pivotcd wipermeans -64 of potentiometer 65; 'fln addition to wiper T64, potentiometer65 includes aresistor '66. Because device 42-responds to the absolutepressure in .cabin 10, it is located in the said cabin. "The device isso-adjusted that wiper 64 is at the right extreme of resistor fi fi atan absolute pressure of 30 inches of mercury and is moved to the leftextreme of resisto'rtfi'upona decreasein theabsolute pressure to 17inches of mercury, .foriinstance.

"Controlp'anel' 13, asshown in Figures 1 to 3 and 6, includes amanualadjustihgknob 71?,a movable index 71, a'lr'atc con'trol'72, land'apushbutton-switch 73-for aligning the iin'd'eflwi'ih lthe llocal barometricpressure and for otherwise testing the system on the ground. The panel431 soinludefsia low pressure or power failure signal light'7f4,;aisignal.light.7,5 'for indicating when the outflow valveliswide-open, and a signalilig'ht 76 for indicating thatthe.rnanualloy'erride is being used. In. Figure 6 no attempt made toarrangelth'e component parts of control pan 3lin ihenian'ner shown inFigure 1 because of the added complications in .the wiring diagram thatwould result. is best shown in "Figures 2 and 3, knob 7%) is fi'x'edltoa sh'a'ft' .7 which carriesan arm 73, preferably of 'lfand to which] isattached atits outer end a contactmeans79. "Shaft 77 is journaied intube 80 and has its right extreme supportedby frictional bearingmeansfili the-frictional bearing means being provided for"'tardingrotation .ofshaft 77 so that knob '70 and con ctineans79willremain in anyadjustecl position in spite i ftsprfing :means 89,,tobe described. Tube 819 is journaled inb'eafing portion 81' of the frontwall 82 of panel '43 and is Tfi'xdly attached to index 71 at its leftend. A .relativelylargeigear83 preferably of Bakelite or thelike, 'is'keycdlto tube .80 for rotation therewith so that gear '83 and'index'71rotate .in unison. A resistor 84 of potentiometer 85 is mountedadjacent the said front wall 82 anclis swept over by wiper'86f carriedby said gear 83. A pair of supporting bracket members 87 and 88 areloosely-iournaled on tubes!) and are urged toward each other bIyIa-coilspring 89. Bracket 87 carries an insulating block T91 which .in 'turncarries an electrical contact 92, while bracket 88 carries .a block 9.3which in turn carries an.electricalcontactIM. "Contacts'92 and 94 arearranged to align .withcontact means79,b.utin a neutral position, theya'refheld in slightly spaced relation from said contact means .79 by aspacer member 95 attached to gear 83 and extending between blocks 91 and.93.

Gear 83 .is driven bypinion 96 whichin .turn is driven by ggeare'd motormeans 97. .Motor .means 97, for the purpose of this descr'iptiom-ispreferably a controllable speedrevers'ible directficufrent ;motor of asort having gobdvai'iable speed characteristics when the voltageapplied. to the same is vafiiedhyba.simplerheostat. Obviously, areversible capaeitorhtype .A. C. imotor :may besub'stitutedfo'rthismotor, for an'yother suitable controllable'speedmotor may be used. As will be made clear in the subsequent descriptionof the operation of the present mechanism, and as -will'be notedfinFigure'fi, 'the present chaser switch arrangement is used to control theoperation of motor means 97. As will be noted, when knob 79, andtherefore contact means 79, is adjusted in either direction, contact92*o'r94. is engaged and it and its respective bracket member is rotatedabout tube 89 away from the other bracket member, the said other memberbeing prevented from following by member 95 unless motor 97 drives gear83 in the proper direction, which it will do when energized. Thismotionof gear 83 will continue until spacer 95 drives the first namedcontact out of engagement with 79.

index member 71 is preferably of transparent material such as Lucite, orthe like and includes a projecting portion 93 having an indicating line99 which easily permits comparison of the position of the said line andthe underlying indicia. Knob 70 is attached to a plate portion 100 whichincludes an indicatingportion 10l,the portion 101 normally being turnedto align with the proper value shown on the scale plate or indicia for Iselecting a desired cabin pressure, the index member 98 then beingdriven to align with 101 in a manner to be described in the subsequentdescription. Because oflhe difliculties of showing the structureillustrated inFigures 2 and 3 schematically, it is noted that themechanism .in Figure 6 differs in detail from that of Figures 2 and- 3,but is adapted to function in a like manner. :It is'thus considered that.the Figures 2 and 3 apparatus is that intended and the showing inFigure 6 is merely for :describing the operation of the presentmechanism.

In addition to includingthe selector-knob 70 and-index 71, with itsassociated control potentiometer andchaser switch arrangement, controlpanel 43 also includes .a push-button switch 73 for permitting operationof .the present mechanism while theairplane is on the ground andespecially for vthe purpose of aligning the index member 98 with theproper indicia for showing the atmospheric pressure at the altitude ofthe aircraft. In parallel with push-button switch 73 is a laniiing gearswitch 105 operated by linkage 10'4 from:the.landingegear. retractionmechanism in such manner that the switch 165 is opened when the landinggearis down and the said switch is closed when the landing gear isretracted. Etate control means '72 of controllpanel 43 includes arheostat 1435 for controlling the speed of motor means 97, as beforementioned. Control panel 45.31 0 includes a signal light 74 for showinglow pressure or A. C. ,power. failure. This signal light is energizedwhen :relaj means 107 is deenergized, the said .relaydmeans 10.7 beingenergized from the A. C. currentsupply through .a full wave rectifier108 when relay 109 is. deenergized. A capacitor lit) is connected inparallel with winding'll l of ihesaid relay 107 for'dela'ying thedeenergization .of.relay 107 for reasons to be described. As beforenotedpanel 43also includes a signal light 75 to indicate whenthe-outflow valve is Wide-open. The 'energization of light''75Iis1'controlled by switching means associated with the outflow valve,to be described. in addition, afurfther signalllight i6 is provided toindicate when the manual override] Unsupercharged position and the righteirtreme Zposi Switch.

tion, that shown, is the Supercharged position. v bank 116 controls theoperation of motors 19 and 24, switch bank 117 controls the'energization of relay 1'21,

switch bank 118 controls the energizationof motor means 28, switch bank1'19 controls the energi'zat'ionof' relay means 122 which inturn-controls the energizat'ion.

of motor 33 and switch bank controls .tliei.energ'iza tion of relaymeans 123 which controls the "energization of motor means 32.

Outflow valve means 15 includes an outflow passage.

128 and a valve member 129 adapted toregulate the,passage of air throughthe same, the said valve,,-means 129 being carried on a shaft 130.:Shaft .130 is rotatedv by a gear train indicated generally as-131whichzisconnected through-a clutch means .132 to aireversibleelectric motor means 133. Clutch means 132isur,ged-out1of engage.- mentby a spring 134-acting on.-a pivoted lever.135and1is operated intoengagement by a solenoid means 136 when the said solenoid means isenergized. Obviously, the solenoid means 136 has suflicient power toovercome spring 134 so that clutch 132 may be engaged. Gear train 131may also be operated by flexible cable means 137 in a manner to bedescribed. In addition to positioning valve 129, shaft 130 alsopositions wiper 138 along resistor 139 of follow up potentiometer 140and operates switching means (Fig. 6), to be described. Motor means 133may be of any reversible sort but preferably is of the two phasecapacitor type similar to motors 19, 24, etc., previously mentioned.While valve means 15 is shown as a conventional butterfly valve, this isintended to be only illustrative and any suitable valve and operatingmechanism may be used instead of the means shown.

Manual override mechanism 45 is connected to valve means 15 by flexiblecable means 137. Override means 45 includes a hand crank 140 forrotating shaft 141 journaled in housing 142 of the means 45 and whichshaft carries a clutch part 143 normally held out of engagement with amating clutch part 144 by spring means 145. By pushing in on crank 140sufliciently to overcome spring 145 and thus engage clutch parts 143 and144, gear train 131 of outflow valve 15 may be manually operated fromcrank 140 through the flexible cable means 137 to thus provide a manualoperating means for the valve. In addition to crank 140 operating valvemeans 15 through flexible cable means 137, it is noted that means 45includes an indicator member 146 extending through slot 147 in housing142. Indicator means 146 is attached to a gear 148 forming part of agear train 149 which is similar in ratio to gear train 131. Thus,whenever flexible shaft 137 is operated by either motor means 133 orhand crank 140, any rotation of shaft 137 will be reduced and indicatedby indicator means 146. By making both the gear trains alike in ratio,the position of valve means 129 is shown at all times by indicator 146.In its normal operation, with clutch part 143 disengaged from clutchpart 144 by spring means 145, manual override means 45 acts only as anindicator to show the position of valve means 129. Override means 45also includes a single pole double throw switch means 150 which,referring to Figure 6, includes a movable blade 151 and stationarycontacts 152 and 153. Switch means 150 controls the energization of theaforementioned solenoid means 136 for operating the clutch 132 of valvemeans 15, and also controls the energization of relay means 154 andsignal light 76 in a manner to be described. Switch means 150 has beenshown separated from override means 45 in the schematic wiring diagramin Figure 6 for convenience.

The amplifier 46 used in the present disclosure is of any conventionalsort that will reversibly control a motor, either directly or by relays,to cause rotation of the motor in one direction when a signal of onephase is impressed upon its input and to cause rotation of the motor inthe opposite direction when a signal of opposite phase is supplied itsinput. Amplifier 46 includes input terminals 155 and 156, power supplyterminals 157 and 158, output terminal 159, common output terminal 160,and output terminal 161. Relay means 109 is connected between terminals159 and 160 and relay means 162 is connected between terminals 160 and161. When a signal of one phase is imposed upon terminals 155 and 156,one of relays 109 or 162 is energized whereas, if a signal of oppositephase is imposed upon input terminals 155 and 156, the other of the saidrelays will be operated. Relays 109 and 162 control the energization ofoutflow valve motor means 133 and may control, under circumstances to bedescribed, rate motor means 97. While any amplifier of the sortdescribed may be used for the present mechanism, I have found one suchas that described in the co-pending application of Albert P. Upton,Serial No. 437,561, filed April 3, 1942, now Patent No. 2,423,534, to bequite satisfactory.

While a junction box 47 is shown in Figure 1 and is used in thecommercial application of the present system, it is not shown in otherfigures of the drawing because of the added complications that would berequired in the showing of the wiring. The junction box 47 isconventional in nature and may be considered to include the usualterminal strips and any accessory apparatus that can be properly locatedin the said box.

In addition to operating potentiometer means 140, shaft 130 of outflowvalve means 15 also operates switching means 164, 165 and 166. Switchingmeans 164 includes a blade portion 168 and another blade portion 169.Blade portions 168 and 169 engage contacts 170 and 171, respectively,when the outflow valve is wide open and blade portion 168 engagescontact 172 when the outflow valve is in any closed position. Blade 168is so related to contacts 170 and 172 that it always engages one or theother of the said contacts. Switch means 165 and 166 include blades 173and 174 which engage stationary contacts 175 and 176, respectively whenthe outflow valve is wide open, with blade 174 remaining in engagementwith 17 6 during a predetermined initial closing movement of the valveand after 168 has engaged contact 172.

Potentiometers 65, 85 and 140 form part of a compound electrical networkcircuit generally identified as 180. This network circuit, starting fromoutput terminal 181 includes a secondary winding 182 of transformer 183connected across a resistor 184, the left end of which is connected byWire 185 to terminal 181. One end of resistor 139 of potentiometer 140is connected by wire 186 through wire 185 to terminal 181, and the otherend of resistor 139 is connected by wire 187 to wiper 188 which isadjustable over resistor 184. Secondary winding 182 impresses anelectrical potential across resistor 184 and, when wiper 188 is adjustedto the extreme right of resistor 184, a like potential is impressedacross resistor 139. Then, as wiper 138 is adjusted across resistor 139,a variation in potential between terminals 181 and wiper 138 equivalentto the full voltage impressed by secondary winding 182 may be had.However, as will be noted, when wiper 188 is adjusted to the extremeleft on resistor 184, all portions of resistor 139 will be at the samepotential as terminal 181, hence movements of wiper 138 across resistor139 will have no appreciable effect. In the position shown, with wiper188 most of the way across resistor 184 toward the left side, a smallpotential is impressed across resistor 139 hence adjustment of Wiper 138across resistor 139 will cause slight variation in potential betweenterminal 181 and wiper 138. Wiper 188 is made adjustabie on resistor 184to provide adjustable means for controlling the amount of rebalancingthat can be impressed in the said network, potentiometer 140 being arebalance potentiometer, as will be noted. However, because a rebalancepotentiometer tends to introduce droop into the system, it is desirableto use as little rebalancing effect as possible, and in the presentinstance, only enough rebalancing is used to prevent hunting. Under somecircumstances, it may be possible to completely eliminate this portionof the network and connect terminal 181 directly to wire 190 which nowconnects wiper 138 with wiper 86. Continuing with the description of thenetwork 188, wiper 138 is connected by wire 190 to wiper 86 ofpotentiometer 85. Potentiometers 85 and 65 are connected in parallelacross secondary winding 191 of transformer 192 by wires 193 and 194 and195 and 196, respectively. This arrangement will be recognized as aconventional voltage dividing network having input terminals 197 and 198and having output terminals comprising wipers 86 and 64. Primary winding200 of transformer 183 is energized by the circuit: line wire 201, Wire202, wire 203, winding 200, wire 204, wire 205, and line wire 206.Primary winding 207 of transformer 192 is energized by the circuit: linewire 201, wire 202, wire 208, winding 207, wire 209, wire 205 and linewire 206. Output terminal 181 of compound network 180 is connected toterminal 155 of amplifier 46 by wire 210, while wiper 64, forming theother output terminal of the network 180 is connected to input terminal156 of the amplifier by wire 211.

As previously mentioned, the main power supply for the presentapparatus, obtained through line wires 2'01 and 206 is 115 volt 400cycle alternating current. As it is convenient to have some of thisapparatus energized by direct current, a suitable source of directcurrent such as battery 212 is also provided. Obviously, any othersuitable source of direct current may be used such as a motor generatorset, rectifier means, or the like.

To better explain the function of the present apparatus, it will now bediscussed in terms of its operation.

OPERATION In describing the operation of the present apparatus, let itbe assumed that the aircraft containing the same is located on a fieldat near sea level altitude and is being prepared for a flight.Assumingthat the 115 volt 400 cycle alternating current source isenergized, it is noted hat. networ ir uit n ized y va ircu tpreviouslyftraieed. Inadd' on, current, is s'upplied amplifier 4 6,.bythe. circuitt line; wire. 20,1, wire 215, terminal 157, terminal@158,wire. 216, and line wire 206. Further, rec tifier108 is energizedby thecircuit: line wire 206, wire 217.,wire2l8, rectifier 108,.wire219, outcontact 220 of. relay 109,v blade 221 of said relay, wire 222', wire 223andlline wire 201. Relay 107 is energized from rectifier 108 by thecircuit: wire 224, winding. 111, and wire 225. backto rectifier 108.This. circuit resultsinwinding 111 being energized. so that blade 22.6is pulled outof engagement with contact 227 sothatlight 74 is notenergized. As before noted, capacitor 110 is connected in parallelwithwinding lllbetweenwires 224' and'225'.

In addition,.motors,19, only one being shown in Fig. 6 since they areall. connected inparallel', are energized. by thejcircuit: linewire,2;l.-1,]wire 230, contact 175, blade 173, wir'e .231, wire 232,.switch blade 233, contact 2'34, wire 235', wire 236, motor means 19),common wire 237, wire23'8'and line wire'206. This energizes motormeansI9i'na mannerto ,drivethe respective damper means to a vent, closing,position so that the discharge from compressors [twill be deliveredthrough duct means 13 to. the. Cabin 10.. Inaddition, motor means 24 areconnected inparallel with motor means 19 by Wires 239 and 240 andaretherefore energized to operate their dampermeans to aduct closingposition so' that the ram air inlets to duct 13aresealed off, therebypreventing the compressed air from leaking back out through theram airinlets. Motor means 281s controlled by a circuit: line wire 201, wire230, switch means 165, wire 231, wire 3.41, blade 242, contact 243, wire244, motor means 28, wire 245, wire 238, and line wire 206.. Thisenergizes motor means 28 me manner to operate damper means in adirection'to divert the compressed air from compressors 11 directlythroughduct 13 into cabin 10.

Assuming that battery 212 is energizing direct current line-.wires 250and 251, and with the outflow valve in a wide open position, it is notedthat light 75 is energized by the circuit: line wire 250, wire 252,switch blade 174, contact 176, wire 253, wire 254, light 75, wire255,and line wire 251. In addition, relay 121 is not energized, and.relays 122 and 123 are not energized due to the present adjustment ofswitch means. 44. With relay means 122 deenergized, motor means 33 isenergized by the circuit: line wire 201, wire 256, wire 257, blade 258of relay 122, contact 259, wire 260, motor means 33, wire 261, andwire238 to line wire 206. This energizes motor means 33 in a mannertoclose damper means 31 to prevent, leakage of air through outlet means30. Likewise, with relay 123 not energized, motor means 32 iscontrolledby the circuit: line wire 201, wire 256, wire 2.62, blade 263, contact 264, Wire 265', motor means 32, wire 2 6 6, .wire 238 andline wire 206. This energizes motor means 32 in a manner-to drive dampermeans 29' to open position so as to permit recirculation of air throughduct means 14.

' With switch 150 on control 45 adjusted toan .Automatic" position,solenoid 136 associated with valve means 15 is energized by the circuit:line wire 250, wire 268, switch blade .151, contact 152, wire 269,solenoid 136, wire 270, and line wire 251. This energizes solenoid 136in a manner to cause engagement of clutch means 132 so that motor means133 is in driving relation to the gear train 131 and valvemember 129.

With transformers 183 and 192 of network 180 energized, it is noted.that wiper 138 of potentiometer 140 is at the left extreme of resistor139; hence, the said wiper is.,at the, same potential as terminal 181.Therefore, no voltage, is being added to the network by this portion ofthecircuit. Further, it is noted that both wipers 86 and 64 areattheright of their respective resistors and, since they are thusconnected by Wires 194 and 196, they are at the same potential; hence,there is no potential difference between 181 and wiper 64, no inputsignal is being supplied the amplifier, and there is therefore no outputto "energize either of relays 109,0r 162.

In discussing network 180, potential is referred to. However, as isobvious upon'inspection, the present network circuit is energized byalternating current and, as will be clear in the discussionof theaforementioned Upton application, amplifiers of the. sort used dependupon changes in phase'relation of theinput voltage "rather thanupon-mere {voltage difierences. "However, rather than *discussgthepresent network in terms of-phase relations, I it is, much, moreconvenient to discuss thesaid network at aparticular half cycle' instantof timeduring which conventional. direct currentrelations hold true.When considered ongthis basis, it is then proper to discuss the signalfrom the net-work circuitin terms of positive or negative. potential.For convenience, it will be considered at the moment in question thatthe left sides of secondary windings 182' and 191 are negative and theright sides positive in potential. Furthen it will be considered thatwhen terminal 156' is positive relative to terminal 155, amplitier 4.6will operate to energize relay 109 to causean opening, of valve .,v Whreas when terminal 156 is negative relative to terminal 1515, relay 162will be energized to cause a closingmovementof the valve. It'isagainnoted that while the present description will relate to terminal156 being positive or negative relative to 155, in actual practicethenetwork will impose signalson the terminals o'fone phase or anothenandthe present description in terms ofpot'entialis merely a convenient wayof describing the action that takes'plaee. Of. course, if a directcurtient network. be used, this description would also PP Y- With theairplane on the ground, and with outflow valve 15 wide-open, the airpressure in the cabin is the same as that on. theoutside, ,hence bellows62 positions it's.,wiper 64in response to, atmospheric pressure. Now, tomake certainthat index 71, as well as the control pomt for the system,is properly adjusted so that any subsequent. cabin ,pressl'lrizing willtake place from the present starting point, push button switch 73 isactuated to close its contacts. Now, with the outflow valve in wide-openposition and; switch means 164, 165 and 166 in a valve open. position,it is noted that rate motor 97 is energized by thecircuit: line w,ire250, wire 27,0, contact 111, blade 169,, blade 168,. contact 170, wire271, wire 27.2 contact 321,. blade .273, wire 274, motor means 97, wire275 and line Wire .251. This energizes rate motor 97 in. a. direction torotate index 71 counterclockwise and to nove wiper 86' to therigh-tacross resistor 84, or in a. direction to cause a closing. movement of.the outflow valve. jSo long as. wiper '86 is to the left of wiper 64,w1per 641is positive relative thereto and amplifier 46 is energlzedin amannerto drive the valve. open. However, should wiper'86 be to the rightof wiper 64,. the said wiper 641s thennegative'reljative to wiper 86,terminal 156 is negative relative to wiper and the amplifier 46 operates.to drive the valve in alclosing direction. Assummg that theaforementioned operation was sufficient to advance index '71.somewhatcounter-clockwise of the position of. the indicator 101 of knob70, or to advance the indexto a lower altitude thanthe knob is set for,it is noted that this will bring contact 94 in engagement with contactmeans '79 of the chaser switch. Further, assummg that'it was possiblefor Wiper 86 to advance to the r ght of 'wiper64, thus making wiper 64negative relattveto wiperSG and causing operation of the valve in a,closlng direction, it is noted that the initial closing movement of thevalve breaks the engagement of blade 169 andjcontact ,171 and blade 168and contact 170. Further, upon breaking the contact between blade 168with contact' 17.0, contact is immediately made between blade 168 andcontact'j172. Now, when push button 73 is engaged to test the system,rate motor 97 is energized by theicircuitz'line wire 2 50, wire 27 6,wire 277, rheostat 1 06, wire 27,8, blade 55 of dilferential controller41, contact'56, wire 279, blade 168, contact 172, wire 280, switch blade281 of relay 121, out contact 282 of said relay, wire 283, push buttonswitch 73, Wire 284, contact means 79, contact 94, wire 285, wire 286,out contact 237 of relay 154,'blade288 of saidrelay, wire 289, motormeans 97, wire 275and line wire 251. This energizes rate motor 97 in adirection to drive index 71 in a clockwise direction and to advancewiper 86 to the left across resister 84. When wiper 86 is movedsufliciently to the left to make wiper 64 positive relative to the same,amplifier 46 is energized ina manner to operate valve means 15inadirection to open the said valve and then, as the valve ismoved towardwide-open position, blade 168 is movedout of engagement with contact 172thus breaking the testcircuit. 'Thus, it will benoted that the operationof the valve to a wideopen position causes operation of therate'moto'rin a manner to tend to drive the valve toward aclosed position and willthus move the index to a; position slightlyto one side of the pressurebeing indicated by theabsolute pressure device 42 whereas, when pushbutton 73 is then operated, it will tend to cause energization of therate motor in a direction to drive the Wiper slightly to the other sideof the indication equivalent to the pressure being responded to bydevice 42. In this manner, the index will be moved to almost the exactindication of the pressure existing at the field at which place thetesting is being done.

With the index properly located, assume that a flight is about to beginand knob 70 is turned to a pressure equivalent to a 10,000 ft. altitudeand the flight is started. Turning the knob in the direction indicatedbrings contact means 79 into engagement with contact 94 thus tending toenergize the rate motor, as before described. However, with push buttonswitch '73 disengaged and landing gear switch 105 still open, the onlycircuit for energizing the rate motor 97 is that previously describeddue to to the wide-open position of the valve, and which on ergizationimmediately tends to drive the valve just wide-open position. However,with the flight now started, and with a substantially wide-open valve,it is noted that the pressure in the aircraft will tend to fall, thuscausing bellows 62 to expand and move wiper to the left across resistor66. In addition, as the aircraft left the ground and the landing gearwas retracted, switch 105 was then closed. This energizes the rate motor97 by the same circuit as the test circuit controlled by switch 73 whichtends to drive index 71 clockwise and to advance Wiper 86 to the leftacross resistor However, since the energizing current goes throughrheostat 106, the rate motor 97 is driven at a predetermined speed sothat the adjustment is made only .at a desired rate, such as 300 feet ofaltitude change per minute. Assuming that the aircraft is rising at ahigher rate than this, the pressure change in the cabin will tend to beat a higher rate and wiper 64 will tend to be advanced to the leftacross resistor 66 at a higher rate then wiper 86 advances to the leftacross resistor 84. As before noted, when wiper 64 is to the left ofwiper 36, it is negative relative to said wiper 86, and terminal 156 isthen negative relative to terminal 155 and valve means is operated in aclosing direction.

Valve means 15 is operated in a closing direction due to the energizingof relay 162 by amplifier 46 by the circuit: amplifier terminal 161,winding 290, wire 291, and terminal 160 of the said amplifier. Thispulls blades 292 and 293 into engagement with contacts 294- and 295,respectively. Motor means 133 is then energized by the circuit: linewire 201, wire 273, who 296, blade 292, contact 294, wire 297, motormeans 133, wire 298, wire 217 and line wire 306. This energizes motormeans 133 in a direction to close the valve.

Closing valve member 129 of valve means 15 tends to prevent the escapeof air from the cabin and thus causes an increase in pressure in thesame. The increase in pressure tends to contract bellows 62 and driveWiper 64 to the right across resistor 66, or at least to retard theleftward movement of the said wiper across the said resistor. In eitherevent, this tends to permit wiper 86 to be advanced to the left of wiper64-, thus making wiper 64 positive relative to wiper 86 and makingterminal 156 of the amplifier positive relative to terminal 155. Whenthis happens, relay 109 is encrgized by the circuit: terminal 159 ofamplifier 46, wi 301, winding 302 of the said relay, wire 303, wire 291and terminal 160. This pulls blades 221 and of relay 109 into engagementwith contacts 305 and respectively, and causes energization of motormeans 155 by the circuit: line wire 201, wire 223, wire 2223, blade 221,contact 305, wire 307, motor means 133, wire 2923, wire 217, and linewire 301. This energizes the motor means 133 in a direction to drive thevalve member 129 in an opening, direction to thus permit a more rapidescape of air and permit bellows 62 to expand and advance Wiper 64 tothe left across resistor 66.. As thus described, wiper 86 is beingadvanced across resistor 84 at a predetermined rate and valve 15 iscontrolled in a manner to vary the pressure in the cabin substantiallyas called for by any particular position of wiper 36. The position ofwiper 86 thus determines the control point for the present system.Should the cycling operation of the outflow valve means 15 become rapidenough to be termed hunting, ratio selector wiper 188 is moved to theright across resistor 184 to give added effect to follow uppotentiometer 140. Thus, as- .suming that blade 64 is to the left ofblade 86 and is thus negative relative thereto, thereby causing aclosing movement of the valve, it is noted that the closing movement ofthe valve will advance wiper 138 to the right across resistor 139, thusmaking wiper 138 positive relative terminal 181 and adding a positivesignal tending to balance out the negative signal causing the closingmovement of the valve. This stabilizing, or follow-up, action is wellknown in the prior art and is more fully explained in my priorapplication, Serial No. 541,58 previously referred to. As before noted,the amount of follow-up is kept as low as possible due to the well knowneffect of follow-up action introducing droop into the system.

it is noted that energization of relay 109 breaks the circuit torectifier 108. However, due to the very low lag in the present system,relay 109 is normally energized in a pecking manner or for very shorttime intervals. Because of the capacitance of capacitor 110, relay 107will remain energized for a short period of time after the rectifier isdeenergized, this period normally being greater than the time ofenergization of relay 109. However, should the pressure in the cabin besufiiciently low that the relay 109 is energized for longer periods thannormal, then relay 107 drops out and light 74 is energized by thecircuit: line wire 250, wire 228, light 74, contact 227, blade 226, wire229 and line wire 251. Obviously, an A. C. power failure would causelight 74 to be energized in the same manner.

When the aircraft cabin reaches a pressure corresponding to the 10,000ft. altitude called for by the cabin pressure selector chaser switch, itis noted that contact 94 will become disengaged from contact means '79thus breaking the energizing circuit for the rate motor. With theaircraft above 10,000 feet and the cabin pressure at 10,000 feet andwith the index and knob adjustment similar so that no circuit iscompleted through the chaser switch, wiper 86 remains stationary and anypressure change in the cabin will tend to move wiper 64 in a directionto cause an immediate restoration of the pressure, in a mannerpreviously described. it the aircraft should now continue to climb to analtitude such that the differential between the cabin pressure and theatmospheric pressure exceeds 4.6 pounds per square inch, then blade 55will be moved out of engagement with contact 56 by contraction ofbellows 51. When this happens, the circuit to the rate motor 97 whichwould normally be used to increase the cabin pressure is opened andregardless of any subsequent movement of the control knob 70, the cabinpressure cannot be controlled to a higher absolute value. Should thedifferential increase to 4.7 pounds per square inch, contact portion 55of differential pressure device 41 moves into engagement with contact 57thus energizing motor means 97 by the circuit: line wire 250, wire 276,wire 277, rheostat 106, wire 278, switch blade 55, contact 57, wire 311,wire 383, wire 286, contact 287, blade 288, wire 289, motor means 97,wire 275 and line wire 251. This will be recognized as the circuit whichenergizes motor means 97 in a direction to advance index 71 in aclockwise direction and to move wiper 86 to the left across resistor 84.A leftward movement of wiper 86 across resistor 84 tends to make wiper64 positive relative thereto, and, as before noted, this action resultsin an opening movement of valve means 15. The opening movement of valvemeans 15 tends to relieve the pressure and thus reduce the differential.However, should the differential pressure increase to 4.8 pounds persquare inch and thus bring blade 58 into engagement with contact 59,motor means 97 is energized by the circuit: line wire 250, wire 276,wire 316, contact 59, blade 58, blade 55, contact 57, wire 311, wire383, wire 286, contact 287, blade 288, wire 289, motor means 97, wire275, and line wire 251. This energizes motor means 97 in a mannersimilar to that previously described, but with the exception that fullvoltage is applied to the motor 97, rheostat 106 being by-passed, thuspermitting full speed readjustment of the cabin pressure in a directionto reduce the absolute pressure of the cabin and thus reduce the saiddifferential pressure. Upon a reduction of the differential pressure,due to a reduction in absolute cabin pressure or to the aircraftdescending to a lower elevation, the previously described control of therate mo tor will be resumed.

If the airplane should start a slow descent from its high altitude, andknob 70 is adjusted to a lower altitude pressure for the cabin, such asthat corresponding to the altitude of the next field to be used, it isnoted that contact means 79 of the chaser switch will be moved intoengagement with contact 92. This will energize motor means 97 by thecircuit: line wire 250, wire 276, wire 277, rheostat 106, wire 278,switch blade 55, contact 56, wire 279, switch blade 168, contact 172,wire 280, switch blade 281, contact 282, wire 283, switch 105, wire 284,contact means 79, contact 92, wire 320, wire 272, contact 321, blade273, wire 274, motor means 97, wire 275, and line Wire 251. This will berecognized as the circuit which drives index 71 counterclockwise andadvances wiper 86 to the right across resistor 84. Movement of wiper 86to the right thus tends to lead the movement of wiper 64 and in sodoing, tends to make wiper 64 negative relative thereto. As beforenoted, when wiper 64 is negative relative to wiper 86, valve means isadjusted in a closing direction thus tending to increase the pressure inthe cabin.

Now, assume that the aircraft descends at a more rapid rate than thecabin pressure is decreased, so that the aircraft altitude actuallytends to become less than that of the cabin altitude. As the aircrafttends to reach the altitude to which the cabin is being controlled, thedifferential between the cabin pressure and the outside pressurecontinues to diminish; hence, the rate of flow through the outlet valvediminishes, thus tending to retard the desired decrease in pressure ofthe cabin and resulting in slight over pressure of the same. Overpressure of the cabin, as before noted, results in a contracting ofbellows 62. and movement of wiper 64 to the right across resistor 66- orat least an increase in the rate at which it was formerly moving. Thiscauses wiper 64 to become positive relative to wiper 86 which, as beforenoted, controls amplifier 46 in a manner to drive the valve open. Whenthe aircraft is at the same or a slightly lower altitude than the valuefor which the cabin pressure is adjusted, even a wide-open valve can notreduce the cabin pressure. However, since the added pressure in thecabin causes wiper 64 to remain at the right of wiper 86, they valveisdriven in an opening direction until it is wide-open. When the valveis driven to a wide-open position, rate motor 97 is energized by apreviously traced circuit as follows: line wire 250, wire 270, contact171, blade 1'69, blade 168, contact 170, wire 271, wire 272, contact321, blade 273, wire 274, motor means 97', wire 275, and line wire 251.This will be recognized as the circuit which energizes motor means 97 ina direction to drive index 71 counter-clockwise and to move wiper 86 tothe right across resistor 84. This circuit continues until wiper 86 isdriven to the right of wiper 64 so that wiper 64 then becomes negativerelative to wiper 86-. Upon this happening, amplifier 46 controls valvemeans 15 in a manner to close the valve. The initial closing move mentof the valve, however, separates contacts 171-169 and 170- 168 thusbreaking this energizing circuit for the rate motor. circuit for therate motor did not include the rheostat, hence the adjustment was madeat the full speed of the motor and, regardless of the position of thechaser switch, the motor was energized in a direction to drive the indexto a position corresponding to the actual pressure existing in theaircraft cabin.

It will also be noted that whenever the valve is driven to a wide-openposition and thus assumes a controlling effect on the rate motor, light75 is energized by the circuit: 174, contact 176, wire 253, wire 254,light 75, and wire 255. This warns the pilot to proceed with care".

From the above description, it is noted that when the alrcraft goesbelow the altitude to which the aircraft cabin is being controlled, theindex 71 and the control potentiometer 85 are adjusted to correspond tothe. actual altitude of the aircraft during such a descendmg flight. Ifthe aircraft should now resume its upward fli ht, the rate motor will beenergized through contacts 79 and 94 of the chaser switch and throughrheostat 106 by a circuit previously traced. This will adust the controlpotentiometer and index 71 at a controlled rate so that the pressurechange in the cabin will be at the rate desired. In this manner,although it was impossible for the cabin pressure control apparatus Itwill be noted that this energizing line wire 250, wire 252, switch bladeto maintain control when the aircraft went below the controlled altitudeof the cabin, it immediately resumed control of the pressure andmaintained the same on any subsequent upward flight of the aircraft.Without this readjusting of the index and the control potentiometer, andassuming that they remained in their previously adjusted positions, thenthe cabin pressure would tend to change at the same rate as the aircraftuntil the aircraft went above the altitude for which the cabin pressurewas controlled.

Assume now, that for some reason or another it is desired to operate theoutflow valve manually. To do this, switch blade 151 of switch 150 ismoved to its Manna control position, so that blade 151 is in engagementwith contact 153. This breaks the previously described energizingcircuit for solenoid 136, thus permitting spring means 134, as seen inFigure 4, to operate lever 135. in a manner to disengage clutch 132,thus disconnecting motor 133 from the valve. Further, relay 154 isenergized by the circuit: line wire 250, wire 268, switch blade 151,contact 153, wire 323, wire 324, winding 325 of relay 154, wire 326,wire 327 and line wire 251. This energizes relay 154 and brings switchblades 273 and 288 into engagement with contacts 328 and 329,respectively. Also, as light 76 is connected across wires 323 and 327,it is energized and indicates that manual control of the outflow valveis now being eifected. The operation of relay 154 as above describeddisconnects the rate motor from the previously described energizingcircuits and connects the amplifier in controlling relation to the saidrate motor by the circuit: line wire 250, wire 330, wire 331, switchblade 304, contact 306, wire 332, contact 328,. blade 273, wire 274,motor means 97, wire 275 and line wire 251. As blade 304 is recognizedas one of those of relay means 109, and which relay is energized upon arelatively high pressure in the cabin, or when. wiper 64 is to the rightof wiper 86, it is noted that a relatively high pressure in the cabinwill energize a circuit to the rate motor causing it to drive index 71in a counter-clockwise direction and to advance wiper 86 to the rightacross resistor 84. This will continue until wiper 86 reaches thepotential of wiper 64 so that the signal to the amplifier is removed,thus deenergizing the relay 109 and preventing further operation of therate motor in the manner described. The circuit for energizing the ratemotor in the other direction is as follows: line wire 250, wire 330,wire 335, switch blade 293, contact 295, wire 336, contact 329, blade288, wire 289, motor means 97, wire 275, and line wire 251. As will benoted, this energizes the rate motor in a direction to drive index 71 ina clockwise direction and to advance wiper 86 to the left acrossresistor 84. However, since blade 293 of relay 162 is operated to acircuit closing position only when the pressure is low in the cabin, orwiper 64 is to the left of wiper 86, and is thus negative relativethereto, it will be noted that a relatively low pressure in the cabinwill cause an energization of rate motor 97 in a direction to drive theindex and the control potentiometer to'a position corresponding to alower pressure value.

Now, to actually adjust the valve means 15, crank handle is pushed in toovercome s ring so that clutch part 143 en ages part 144, the handlethen being rotated in a suitable direction. This operates flexible cable137 which drives valve means 129 thr ugh gear train 131 in the desireddirection. In addition, the position of the valve will be indicated byindicator 146 in the samemanner as when the valve was automaticallydriven. Due to the li ht 76 bein energized, warning is given that themanual override. is en aged so th t any hand cranking of the val eshould be done with caution. Furth r. due to the forementionedconnecting of the am lifier in controlling relation to the rate motor,the index 71 will indicate at all times the exact pressure existing inthe cabin. Due to the amplifier controlling the rate motor 97 to adiustthe index 71 and the wiper 86 in a manner to cause wi er 86 tocorrespond in position to wiper 64, they are etfectively controlled tonot only indicate the exact pressure in the cabin but to maintain thecontrol point for subsequent automatic control at that indicated value.

The present description has all been based upon a supercharged cabin.Now, if it be desired to operate the cabin in a non-superchargedcondition, switch means dampers 18, 23, 25, 29 and 31.

44 will be adjusted to the unsupercharged position by rotating knob 115in a counterclockwise direction. This switch means, as before noted,controls the position of However, it is noted that the energizingcircuit for motors 19, 24 and 28, corresponding to dampers 18, 23 and25, respectively, is completed through switch means 165 and this switchmeans, as previously noted, is closed only when the outflow valve iswide open. Further, the energizing circuits for motors 33 and 32,corresponding to dampers 31 and 29, respectively, are completed throughswitch means 166, which is also closed only when the outflow valve iswide open. Therefore, regardless of the adjustment of switch means 44 toa different position, none of the dampers effecting the pressure of thecabin can be actuated until the outflow valve is wide open. This is asafety precaution which prevents any decompression of the cabin byoperation of switch means 44: Decompressing of the cabin must be at acontrolled rate by the outflow valve hence, if it be desired todecompress the cabin, the outflow valve must be driven to a wide-o enposition by proper operation of the control knob 70 to reduce thepressure in the cabin to the atmospheric pressure existing outside theaircraft.

Assuming that the outflow valve is now in a wide-open position and thatknob 115 of switch means 44 has been rotated to bring the blades ofswitches 116 to 120 inclusive to the adjacent counterclockwise set ofcontacts, it is noted that motor means 19 and 24 are energized by thecircuit: line wire 201, wire 230, contact 175, switch blade 173, wire231. wire 232, switch blade 233, contact 239, wire 340, motor means 19,wire 237, wire 238 and line wire 206. Motor means 24 is energized inparallel with motor means 19 by a wire 342 connected to wire 340. Also,motor means 28 is energized by a similar circuit as follows: line wire201, wire 230, switch 165, wire 231, wire 241. switch blade 242, contact343, wire 345, motor means 28, wire 245, and wire 238 to line wire 206.Energizing of motors 19, 24 and 28 in the manner described causes themto operate their respective dampers to the opposite position from thatshown. With the new position of switch means 44, relay 122 is energizedby the circuit: line wire 250, wire 252, blade 174, contact 176, Wire253, wire 346, wire 347, temperature responsive switch 348, wire 357,contact 349, switch blade 350, wire 351, winding 352 of relay 122, wire353, wire 354 and line wire 251. Energizing relay 122 causes anenergization of motor means 33 by the circuit: line wire 201, wire 256,wire 257, blade 258, contact 355, wire 356, motor means 33, wire 261,and wire 238 to line Wire 206. Thus, providing the temperatureresponsive switch 348 is in a circuit closing position, motor 33 will beenergized in a manner to open damper 31 and thus dump recirculated airto the outside. As the temperature responsive switch 348 comprises nopart of the present invention, it will not be further discussed here.

Motor means 32 is energized under control of relay 123, as beforementioned. Relay 123 is energized by a circuit as follows: line wire250, wire 252, blade 174, contact 176, wire 253, wire 346, wire 347,switch 348, wire 357, Wire 358, contact 359, blade 360, wire 361,winding 362 of relay 123, wire 354 and line wire 251. This energizesmotor means 32 by a circuit: line wire 201, wire 256, wire 262, blade263, contact 363, wire 364, motor means 32, wire 266, and wire 238 toline wire 206. This circuit energizes motor means 32 in a direction toclose oil" the recirculation of air simultaneously with the opening ofdamper 31. However, since this circuit also goes through temperatureresponsive switch 348, this recirculation is prevented only when thetemperature responsive switch so permits.

Relay 121, assuming that valve 15 is in a wide-open position, is alsoenergized by a circuit traced as follows: line Wire 250, Wire 252, blade174, contact 176, Wire 253, wire 346, wire 371, blade 372, contact 373,Wire 374, winding 375 of relay 121, wire 376 and line wire' in automaticoperation, is in a wide-open position. When the outflow valve is in awide-open position, the rate motor is energized by a previously notedcircuit going through:

switch means 164 which energizes the said motor means 97 in a directionto cause a closing movement of the valve means 15 whenever wiper 86 isadvanced to the right of wiper 64 and at the same time is correctlypositioning index 71. Now, as before noted, when wiper 86 is driven tothe right of 64, amplifier 46 is controlled in a manner to drive thevalve toward closed position thus breaking the previously noted circuitenergizing the rate motor. Moreover, assuming that the aircraft isrising, the resulting movement of wiper 64 to the left tends to make itnegative relative to wiper 86 thus also causing operation of the valvemeans in a closing direction. However, upon the valve moving from thewideopen position, relay 121 remains energized by the above notedcircuit due to blade 174 remaining in engagement with 176 for a greatervalve movement than is required to operate switches 164 and 165. Withblades 281 and 377 of relay 121 in engagement with contacts 378 and 379,respectively, a circuit is then completed energizing rate motor 97 asfollows: line wire 250, wire 276, wire 277, wire 380, switch blade 377,contact 379, wire 381, switch blade 55, contact 56, wire 279, switchblade 168, contact 172, wire 280, blade 281, contact 378, wire 382, wire383, Wire 286, contact 287, blade 288,. wire 289, motor means 97, wire275 and line wire 251. This will be recognized as a circuit whichenergizes rate motor means 97 in a manner to adjust index 71 in aclockwise direction and to move wiper 86 to the left across resistor 84.Further, this adjustment will be made at high speed because the rheostat106 is by-passed. As wiper 86 is moved to the left of wiper 64, wiper 64becomes positive relative to wiper 86, terminal 156 becomes positiverelative to 155, and amplifier 46 controls motor means 133 in a mannerto adjust valve 15 to a wide-open position. When the valve is adjustedto a wide-open position, switch blade 168 is moved out of engagementwith contact 172 and into engagement with 170 as before. This breaks theaforementioned energizing circuit for the rate motor and re-establishesthe previously mentioned circuit which again drives motor 97 in a mannerto readjust the outflow valve away from open position. Thus, when theswitch means 44 is adjusted to any of the unsupercharged positions,relay 121 is not only energized when the valve is in a wide-openposition but remains energized during the initial closing movements ofthe valve sufliciently to control a circuit to cause the valve to againbe opened to its extreme, while other switch means are available fordriving the valve to a partly closed position whenever it reacheswide-open position. However, all of this controlling action is based onwiper 86 moving to one side or the other of wiper 64, hence the positionof wiper 64, a function of the absolute cabin pressure, determines thepoint at all times about which the rate motor will control the index;therefore, the index must always keep step with the actual cabinpressure in the airplane. Because the index always keeps step with theactual pressure in the airplane, the potentiometer is always adjusted sothat if it be decided to supercharge the cabin and switch means 44 is soadjusted, then the change can be made Without any sudden pressurechanges and further changes in cabin pressure can be made at acontrolled rate without delay.

It is thus noted that the present cabin pressure control system will notonly function to maintain a given cabin pressure, but will effectchanges in cabin pressure at a controlled rate. Further, upon theaircraft descending in altitude below the controlled altitude of thecabin, the control point will be shifted in accordance with the alti'tude of the aircraft, with a signal being given to the pilot to takecare, and any subsequent rise in altitude of the aircraft will permit achange in the cabin pressure only at the controlled rate unless, ofcourse, the limiting pressure differentials are exceeded. When thelimiting pressure 'diflerentials are exceeded, it first becomesimpossible to adjust the cabin to a hi her absolute pressure, next'alower absolute pressure is called for by the apparatus and then if thedifferential pressure still further increases, the readjustment to alower absolute pressure is made or" the full speed of the apparatus.

Also, if the aircrait be flown in an unsupercharged condition, theoutflow valve motor will be controlled in a manner to hunt" about itswide-open position and the rate motor will be controlled to adjust theindex and control point in accordance with the absolute pressure in theaircraft. Also, if the outflow valve be manually controlled, the

angers amplifierwhichsnonnally controls rneomfiowmve motor will beswitched into controlling rrelation tto the rate motor to thus adjustthe: indexzand controlpoint inaccorda'nce with the absolute' pressurein' the cabin;

Provision is" made for testing the apparatus on the ground beforebeginningthe flight and, except during,

testing, changes'incabin pressure cannot be'made until tlieaircraftleaves thegroun'd andthe landing gear is retracted: As safety features;signal'means are provided for indicating low pressure in the cabin, lackof'A': C. power, a Wide-openoutfiow valve, and control of the outflowvalve bymanua l means: As=additional safety means, the switchingapparatus controllingthe pressure seals and the like of 'the'cabinare'socon'elated with the outflow valve tliat no changeinthesupercharged condition of thecabin can beefiectedunles'sthe outflowvalveis in a wide-open position.

While the presentinventionliasbeen rather specifically described; itisobvious that'tliere are many substitutions and equivalents that'canbeused, hence the scope of this invention isto be determined only by theappended claims.

I claim as" my invention:

1. Cabin pressure control apparatus for an aircraft including, incombination, outflow valve means; controller means for saidvalve means,motormeans for adjusting said controller means, manual means foradjusting the direction and extent-of'travelof saidmotormeans, means foradjusting tlie speed of travel of said motormeans, means responsive tothe dilferential of the pressure existing in the aircraft'cabinandtheatmosphericpressure surrounding the said'cabin, saiddilferential'pressure responsive means including switching meansoperable to first prevent further operation of said motormeans in adirection to adjust said controller means in a manner to increase thesaid differential and operable at'a higher value of. thesaiddiiferential'to causeoperation of said motor means'in a manner to reducethe said differential and operable at a still higher valueofsaiddifferentialto cause said motor meanstoadjustsaidzcontroller meansat high speed in" a direction toreduce said differential, and meansoperable'as an incident to the operation of said Valve meansto awide'openposition for causing said motor meansto adjust saidcontroller'meansin a direction opposite to that caused by saiddifferential pressure responsivev means.

2; Cabin pressurecontrol apparatus for an aircraftiineluding, incombination, outflow valve means, amplifier meansfor controlling saidvalve means, network circuit means forcontrolling said amplifier means,absolute pressure" responsive means for adjusting said networkmeans,control point adjusting means for adjustingsaid network means, motormeansfor adjusting said control point adjusting means, manual means forcontrolling said motor means, means for regulating the speed. bywhichsaid motor means can adjust said control point. adjusting means, meansresponsive tov the diiferential' between the cabin air pressure and theatrnospheric'air pressure, said differential responsive means includingmeans operable to controlsaid motor means, means .for switching saidamplifier means out offcontr'ol ofsaid valve meansand in controllingrelation to said'motor means, andmeans operable as an incident. to theadjusting of said valve means to a predetermined'limiting position forcontrolling said motor means.

3.. Control apparatus for a pressurized aircraft cabin I comprising, in.combination, pressure controlling means,

controller means including a device responsive to cabin pressure forcontrolling said pressure controlling means,

manually, adjustable means for adjusting said controller,-

means and thus said. controlling means, and means foreffectively-causing said pressure responsive device to adjust said.manually adjustable means.

4. Control apparatus comprising, in combination, a

positionable. control device operable between limiting:

5i Control apparatus comprising, in combination, a

positionable control 5 device; means responsive to a: conditionindicative of aneed: for [positiongll positioning saidideviceforcontrolling said device, meanstor'adiusb ing" said condition responsivemeans, and switching means operable as a function of "a predeterminedpositioning 1 of said device for placing said conditionresponsive: meansin control of said adjusting means- 6. Apparatus for controlling acondition comprising, in combination, a condition controlling device,adjustable meansresponsive'to said condition for automaticallycontrolling said 5 device, manual means for operating said device, othermanual means for causing adjustment of saidcondition responsivemeans ata timed rate', means for indicating'the saidadjustrnent at any instance;and switching means, for transferring control by said" conditionresponsive deviccof saidcontrolling'deviceto.said indicating means whensaid controlling dcvice'is manually operated, said indicating means thenindicating, the value of said condition;

7; Control apparatus comprising, in combination, a condition controlmeans, condition responsive means, means connectingsaid conditionresponsive means incontrolling relationto saidcontrol-means, means forindicating and adjusting the" controlling affect .ofsaid conditionresponsive means on saidcontrol means, motor meansfor adjustingsaidadjus'ting means, manuallmean's. for normally controllingsaid'motormeans, and-means for connecting said condition responsivemeans, in controlling relation. to said motor, means.

8. Control apparatus comprising, in COHibl-I1aiiC 1n,',& conditioncontrol means, condition, responsive. means, means connecting said'condition responsive means. in controlling relationlto said controlmeans,.means..for;ii1- dicating and adjusting the. controlling affectof-said' condition responsive meanson said control means,- motor meansfor adjusting said adjusting means, manualrme'ans for normallycontrolling, said motor means, additional manual means. for operatingsaidconditioncontrol'meaus,

and means. for rendering said additional manualrmeans efiective and forconnecting said'condition responsive means inicontroiling relation tosaid motor' means.

9. Control apparatusforcontrolling. a, conditiorrir'rv a space in'relation'to a similar condition outside. of said space including, incombination, an adjustable. control device, motor means for adjustingsaid'device, means-for normally controlling said motor means in .amannerto permit it to operate at. a predetermined fractionof. its full speed,and differential condition responsive. means I responsive to apredetermined relatively high .value or the condition inside said spacerelative to the condition outside said space for causing said'motormeans ton-adjust said. control device to operate at its full speedin..a,dir'ection to cause a reduction inthe value oftliesaididifierential.

10. Control apparatus for controlling a condition ina space in relationto a similar condition outside, of said space including, in combination,a conditioncontrolling means, an adjustable control device forregulating the operation ofsaid controllingmeanarnotor meansforadjusting said. device, means for normally controlling said motor. meansin a manner to permit it. tooperate. at. a predetermined fraction of itsfull speed to permit said device. to [relativel relatively slowly adjustsaidl controlling mcans, and differential condition responsive. meansresponsive to a predetermined limiting value of. the. condition insidesaid space relative to tlie condition, outside of said space. forcausing" an immediate adjustingofl said control ing'means in a manner toreduce the value of'tlie said difierential.

11. Apparatus for controlling air pressure. jnanaircraft cabincomprising, in combination, outflow valve means, other valve means forcontrolling. the pressure of air in the cabin, means for controllingsaid: outflow valve means in.a manner. to maintain a predeterminedpressure With'in-saidlcabin, and switching means permitting eitheropeningor. closing ofsaid othervalve means only when said outflow valvemeans is in at W-ideropen position, at least a portion of said switchingbeingoperable in accordance withthe wide-open positioningof saidouttlowvalvemeansl 12. Apparatus for: controlling the pressure-of. airin the cabin of'tanaircraft' including, in combination, outflowvalvemeans, controllermeans for said valve means, motorimean's foradjustingsaid controller. means, manual means for adjusting said motor means,differential pressure responsive means for controlling said motor means,means operable as an incident to positioning said outflow valve means ina wide-open position for controlling said motor means, means forindicating that said valve means is in a wide-open position, means forindicating a relatively low pressure in said cabin, manual means forcontrolling said outflow valve means, means for indicating the controlof said outflow valve means by said manual means, and means preventingthe control of said motor means by said manual means when the saidoutflow valve means is being manually adjusted.

13. In apparatus for controlling a condition in a space; adjustablemeans for varying said condition, said adjustable varying means beingoperable between limiting positions; actuating means for said varyingmeans; and control means for said actuating means, said control meansincluding apparatus responsive to said condition, means connecting saidcondition responsive apparatus in controlling relation to said actuatingmeans, means for adjusting the controlling relation between saidcondition responsive apparatus and said actuating means to thereby varythe [valve] value of said condition to be at tained, and means operableas an incident to said varying means reaching one of its limitingpositions connected to adjust said controlling relation adjusting means.

14. In control apparatus for controlling one condition relative to asecond condition; means for varying said one condition; means forcontrolling said varying means, said controlling means includingapparatus responsive to said one condition; motor operated means foradjusting the controlling relation between said condition responsiveapparatus and said varying means to thereby adjust the value of said onecondition at which said apparatus is in eflective control; means foradjusting the rate at which said motor operated means can adjust saidrelation; and means responsive to a predetermined differential betweensaid one condition and said second condition connected through said rateadjusting means for causing operation of said motor operated adjustingmeans in a direction to reduce said differential.

15. Control apparatus comprising, in combination, a conditioncontrolling device, means for controlling said device includingcondition responsive means, means for causing cycling operation of saiddevice, and indicating means controlled by said controlling means andenergized only upon a predetermined change in the operation of theoperating cycles.

16. Apparatus for controlling air pressure in an aircraft cabincomprising, in combination, an adjustable valve means for controlling aflow of air into said cabin, valve means for adjustably controlling airflow out of said cabin for maintaining predetermined pressure in saidcabin, switching means operable by said outflow valve means at apredetermined outflow valve position, control means for adjusting saidfirst named valve means, and means connecting said switching means incontrolling relation to said control means.

17. In apparatus for controlling the pressure of air in an aircraftcabin or compartment having at least one opening for the flow of air,which flow determines the said pressure, the combination of: airflowmeans adjustable so as to effect different flows of air through saidopening and thereby produce different pressures in said cabin; controlmeans for said airflow means operating to effect through said airflowmeans a desired pressure of air in the cabin, said control means havingcontrol parts of adjustable correlation, the instant correlation of saidparts determining the instant adjustment of said airflow means; jmeansoperative to adjust said control parts so as to change the correlationof said control parts so as to obtain a difierent adjustment of saidairflow means; an overriding control operative to adjust said controlparts so as to change the instant correlation of said control parts to acondition of correspondence with ambient air pressure; means foractivating said overriding control; and a second overriding controloperating when a predetermined pressure difierential of cabin pressureover ambient pressure is exceeded to change the correlation of saidcontrol parts and accomplish an adjustment of said control means to avalue which is within a predetermined diflere ntial from the instantambient pressure.

18. Control apparatus comprising, in combination, a condition controlmeans, condition responsive means, means connecting said conditionresponsive means in controlling relation to said control means, meansfor adjusting the controlling efiect of said condition responsive meanson said control means, motor means for adjusting said adjusting means,manual means for normally controlling said motor means, and means forconnecting said condition responsive means in controlling relation tosaid motor means.

References Cited in the file of this patent or the original patentUNITED STATES PATENTS Number Name Date 1,832,809 Hudson Nov. 17, 19312,038,431 Klages Apr. 21, 1936 2,119,402 Putter May 31, 1938 2,208,554Price July 16, 1940 2,244,722 Norcross June 10, 1941 2,276,448 Allen etal Mar. 17, 1942 2,307,199 Cooper Jan. 5, 1943 2,346,437 Krogh Apr. 11,1944 2,399,326 Crot Apr. 30, 1946 2,401,832 Krogh June 11, 19462,407,257 Del Mar Sept. 10, 1946 2,407,540 Del Mar Sept. 10, 19462,413,027 Maxson 2. Dec. 24, 1946 2,419,707 Cooper et a1. Apr. 29, 19472,424,491 Morris July 22, 1947 2,450,881 Cooper et a1. Oct. 12, 19482,463,489 Kemper Mar. 1, 1949 2,473,776 Baak June 21, 1949 2,484,847Paget Oct. 18, 1949 FOREIGN PATENTS Number Country Date 521,623 GreatBritain May 27, 1940

